<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>编程思想</title>
</head>
<body>
    <h2>分层结构</h2>
    <ul>
        <li>结构层 HTML</li>
        <li>表示层 CSS</li>
        <li>行为层 JS</li>
    </ul>

</body>
</html>